This invention relates to pressure fluid operated impact tools particularly adapted for use in mechanically operated drills of the percussive type such as used in rock drilling and similar operations. The invention is particularly adapted to those applications where the diameter of the drill body is limited as for instance those cases where the drill is adapted to follow the drill bit down the drill hole. In such cases, of course, the diameter of the drill is limited by the diameter of the drill bit and it must be somewhat smaller not only to get into the drill hole but to permit the escape of drill cuttings.
Three of the primary considerations for such drills are high energy output, simplicity and reliability of construction, and ease and cost of replacing parts worn by impacting or abrasion. It is accordingly an object of this invention to provide a fluid actuated impact tool of the type described which is powerful, of simple and reliable design, and constructed in such a manner as to permit ready disassembly and replacement parts. It is a further object of this invention to provide an impact tool having a minimum of parts and constructing such parts as are required in a manner which minimize their difficulty of fabrication and cost. It is an object of this invention to eliminate as much as possible off center axially drilled porting and to replace it where possible with surface machined porting such as circumferentially machined grooves.
It is a further object of this invention to obtain maximum energy output from the impact piston by having it strike directly on the percussive bit and further to apply a constant pressure in the direction of impact on the outer surface of the piston. The impact mechanism is comprised of only one moving part and all valving of the pressure fluid is accomplished by the unique internal and external porting of the piston. It is a further object of the invention to provide a casing which is reversible to obtain maximum life utilization. By reversing the casing, it is allowed to experience the maximum wear near the bit on both ends of the sleeve.
Accordingly, it is an object of this invention to provide a percussive drill apparatus comprising: a casing extending substantially the length of the drill apparatus; a backhead disposed at one end of the casing for connecting the drill apparatus to a drill string and source of pressure fluid; a distributor disposed within the casing at one end of the casing; a percussive member disposed at the other end of the casing to form a chamber between the distributor and the drill bit within the casing; a cylinder sleeve disposed with radial clearance in the chamber toward one end to form an annular passageway; and a piston disposed in the chamber for reciprocating axially therein and imparting a blow on the drill bit; the piston being in sliding contact with the cylinder sleeve towards one end and in sliding contact with the casing towards the other end. Other objects and advantages of the construction will be in part pointed out and in part obvious hereinafter in the description of the preferred embodiment illustrated and in the drawing.